Which evidence from the text best supports the idea that lady Macbeth believes that Macbeth wont be strong enough to kill the king and further his own ambitions?

Macbeth Act 1 scene 7: (lady Macbeth) : any news?

(Macbeth):

"We will proceed no further in this business.

He hath honored me of late, and I have bought

Golden opinions from all sorts of people ... "

Thus, Macbeth was a coward - he was elected as Crown by Duncan, in result Macbeth did not want to kill Duncan.

Art not without ambition, but without / The illness should attend it.

I took apex.